So - a short review: Its a stealth game through and through with scaling difficult on the ballistics and how intelligent the NPC's are. The harder the difficulty, the more you'll need to use your wits and the environment to complete the missions.
There's 8 stages, which are open - so there are multiple approaches you can take to complete them. Only 1 is linear like previous games. On the easiest difficulty you can complete a stage in about 30 minutes. On the hardest it too much over 3 hours to complete one. Mainly because I died so many times! Leave all notions of history at the door, the idea is you travel through North Africa, stopping the Nazi's (and some Italians) and their evil plans, while saving the British and generally being 'Murica fuck yeah! Oddly the game is made in the UK yet this game has the same stereotypes as COD type games.
Unlike previous games, there are multiple objectives which you can chose to do or simply ignore. Spread across maps are other collectables, which in turn will allow you to unlock weapons and upgrades.
In the previous games you could make a basic selection of weapons, in this one you can customise your rifle to a degree but its not like a BF game with a large degree of customisation.
You also get some challenge modes which are survival type affairs. With co-op, you can play through most of the missions and a couple of different survival modes. One of which is one player is the spotter (spotting in Sniper Elite is important). There is also a MP mode but I've not tried it so can't comment.
Overall, it's got plenty of replay value, especially when you factor in co-op modes. The missions are large enough that they can provide different routes to complete them in different ways each time. Also, what really sets it apart from any other game is the kill cam. Just look on Youtube for videos of Nazi's having their nuts shot off.
Payday 2 is actually a very similar game in many respects! SE3 is still full price with a season pass for DLC. Payday 2 is usually on some kind of sale. I picked up the game plus all DLC for 12 quid! Which is a bargain.